Discovery and analysis of Bartonella henselae antigens for use in clinical serologic assays.

The antibody response to Bartonella henselae has been studied in a number of mammals; however, the human response needs to be further studied. After natural infection, humans have antibody reactivity to a large number of B. henselae proteins. We used a proteomic approach to identify antigenic proteins of B. henselae to determine their capacity to elicit a human antibody response. Comparing patient sera by Western blot analysis demonstrated significant amounts of reactivity to B. henselae. The immunofluorescence assay (IFA)-positive sera identified several protein spots of interest. However, a consistent reactivity to a single spot by all sera was not observed. Three of these spots demonstrated reactivity in 71%, 64%, and 64% of positive sera tested with negligible reactivity to the negative sera. These proteins were identified as GroES, BepA, and GroEL. Most IFA-positive sera demonstrated reactivity to GroES, GroEL, and BepA. The usefulness of these proteins for a clinical serologic assay is discussed.

Cross-reactivity of human immunoglobulin G2 recognizing phosphorylcholine and evidence for protection against major bacterial pathogens of the human respiratory tract.

Phosphorylcholine (ChoP) is an antigenic component on the cell surface of many commensal and pathogenic bacteria that reside in the upper airway. In the present study, human ChoP-specific antibody was affinity-purified from pooled serum gamma globulin. This naturally acquired antibody, which is primarily of the immunoglobulin (Ig) G2 subtype, recognized ChoP on the lipoteichoic acid of Streptococcus pneumoniae and on the lipopolysaccharide of Haemophilus influenzae, 2 of the leading etiologic agents of infection involving the human respiratory tract. In in vitro killing assays, anti-ChoP IgG2 was effective against some clinical isolates of nontypeable H. influenzae and against isolates of several common serotypes of S. pneumoniae. Moreover, passively administered human anti-ChoP antibody protected mice against lethal challenge with a transparent isolate of S. pneumoniae type 6A. The effectiveness of human antibody to this conserved bacterial structure suggests that, if it can be manipulated to broaden its activity, it could function as a single vaccine antigen that targets multiple pathogens.